Manufacture of propeller blades



Nov. 17, 1942.

G. T. LAMPTON MANUFACTURE oF PROPELLER BLADES vFiled April 13, 1959 2 Sheets-Sheet 1 Z C JK Nov. 17, 1942; G, T LAMPTQN 2,302,229

MANUFACTURE. OF PROELLER BLADES Filed April l5. 1939 2 Sheets-Sheet. 2

Patented Nov. la7, 1942 MANUFACTURE F PROPELLER BLADES Glen T. Lampton, Williamsport, Pa., assignor. by

mesne assignments, to The Aviation Corporation, New York, N. Y., a corporation of Dela- Ware Application April 13, 1939, Serial N0. 267,548

Claims.

The invention relates to the'manufacture of hollow metal propeller blades for aircraft from tubular steel blanks.

In the production of hollow steel propeller blades from tubular blanks it is desirable to vary the wall-thickness of diiierent portions of the blank, more particularly, those used in forming the suction and pressure face-members, so that the resulting Wall-thickness in the finished blade will be proportionate to the high and low stresses to which the different portions 0f the blade are subjected in use and also for weight-saving purposes. It is desirable in the manufacture of these blades to employ a tubular blank having an approximately uniform wall-thickness as great as the thickest section required in the finished blade and to cut away metal from the portions of the exterior surface in producing the zones of reduced wall-thickness by machining or grinding operations. It is lof great importance in the machining or cutting operation to accurately control the removal of the metal to produce the predetermined wall-thickness desired and to avoid any deviation from the proportionate thickness for producing the necessary strength in the dilierent portions of the blade.

Another factor encountered in manufacturing hollow blades from tubular steel blanks is the commercial variations or irregularities in the geometric shape of the blanks.

In reducing the wall-thickness of a tubular blank it has been found desirable to support the blank on a solid arbor fitting the internal periphery of the blank. Unless the blank closely surrounds the arbor during the machining operation, the relatively thin wall of the blank may be ing the' metal from the blank. Commercial irregularities in the shape or wall-thickness of the tubular blank, when the blank is placed on an arbor and subjected to predetermined machining operations, result in undesirable irregularities in the wall-thickness of the blank. When the arbor is driven into the blank, the internal periphery of the blank and the external periphery of the arbor are galled or otherwise damaged. For these reasons, the methods heretofore used, to my knowledge, have resulted in undesired variations or irregularities in the wall-thickness of the blank or in failing to produce a true fit between the blank and the arbor for external machining operations.

When a tubular blank is shrunk onto and removed from the arbor by heating the blank, al-

deformed or bent by the tool employed in removlowing it to cool on the arbor and reheating the (Cl. .Z9-156.8)

blank for its removal from the arbor, certain allotropic and chemical changes occur in the metal which produce physical changes such as a partial hardening of the metal which renders it undesirable for machining and that unless the shrinking and cooling of the blank are controlled within certain limits the metal of the blank will be difcult to machine.

One object of the invention is to provide a method of manufacturing propeller blades from a tubular steel blank which comprises shrinking the blank on an arbor in such a manner that the exterior dimensions oi the blank will be machined to produce accurate predetermined varying wallthicknesses by conforming the internal periphery of the blank accurately to the periphery of the arbor during the machining operation so as to avoid deviation from the predetermined wallthickness desired.

Another object of the invention is to provide an improved method of controlling the shrinkage and expansion of the tubular blank in fitting it around and removing it from the arbor so as to maintain the desirable machining characteristics of the metal in the blank after it has been removed from the core or arbor.

A still further object of the invention is to provide a method which comprises shrinking the tubular blank onto an arbor in such a manner that an internalirregular periphery will be reshaped into the desired contour and irregularities in the internal periphery of the blank will be eliminated so that the machining operations can be performed on its external periphery to produce the predetermined variations in wall-thicknesses desired.

The invention consists in the several novel fea- -tures hereinafter set Lforth and more particularly defined by claims at the conclusion hereof.

In the drawings: Fig. 1 is a side elevation of the tubular blank used in making the'hollow propeller blade. Fig. 2 is a longitudinal section of the tubular blank after it has been upset and swaged. Fig. 3 is a side elevation of the arbor onto which the blank is shrunk. Fig. 4 is a section of the blank shrunk onto the arbor. Fig. 5 is a side elevation of the blank on the arbor after the blank has been machined to vary the wallthckness of different portions of the blank. Fig. 6 is a section of the arbor and blank on line 6 6 o1 Fig. 5 in a lathe for cutting portions from the wall of the blank. Fig. 7 is a section through the arbor and blank taken on line 1-1 of Fig. 5.

Otherobjects of the invention will appear from the following description.

Fig. 8 is a plan of the blank after it has been machined and bent longitudinally so that one side will conform to the contour of the leading edge of the blade. Fig. 9 is a transverse section illustrating the flattening of the blank between dies. Fig. 10 is a plan of the blank after it has been flattened. Fig. 11 is a transverse section of the blank while cut marginal portions are being welded together for forming the trailing edge of the blade. Fig. 12 is a transverse section of the Welded blank after it has been expanded to shape the outer surfaces of the pressure and suction faces substantially to airfoil form. Fig. 13 is a plan of the finished blade. Fig. 14 is a section on line Iii-i4 of Fig. 13. Fig. 15 is a graph illustrating the temperatures incurred in expanding the blank to receive the arbor and shrinking the blank onto the arbor.

The invention is exemplified by the manufacture of the blade from a tubular blank a of requisite length and having a commercially uniform wall-thickness at least as great as the wallthickness desired in the leading and trailing edge `portions of the finished blade. One end of the blank is swaged and upset to form a shank portion b and a tapering portion c, joining the shank portion and the cylindrical section d from which the pressure and suction faces of the blade are shaped.

A solid arbor or core e is provided for insertion into the blank after the latter has been shaped to form shank b, tapering portion c and section d. The contour of the periphery of the arbor corresponds to the contour desired for the inner periphery of the blank while it is being machined and its area is at least slightly greater than that of the normal area 4of the internal periphery of the blank, so that when the blank is shrunk onto the arbor the inner periphery of the blank will conform accurately to the arbor and the blank will be rigidly secured thereon. 'I'he arbor e is provided with studs el for centering it in a suitable lathe used for machining zones of metal from the outer face of the blank on section d to produce reduced wall-thickness where desired according to the stresses to which the different portions of the blade are subjected.

Before the blank is shrunk on the arbor it is heated to a suiilciently high temperature so that Y the expansion of the tubular blank will exceed the limits of its inaccuracies or irregularities and permit the cold arbor to be inserted and positioned in the blank withoutl interference.- In this heating of the blank the invention involves temperature control so that when the blank shrinks onto the arbor, or cools at relatively low temperature it will not expand abruptly away from the arbor and lose its previous tight t on the arbor when both the blank and arbor are subsequentially brought to normal temperature. The invention contemplates the expansion of the blankby keeping the temperatures within certain limits so that Fig. 15. These critical temperatures are referred alloy has the following approximate values of the critical temperatures:

Aci 1360 F. AT1 830 F. Ac: 1530 F. Ars 990 F.

When iron or iron alloys are heated from a low temperature they progressively pass through several critical temperatures, as shown graphically in to in the metallurgical art as Aci, Ac'z, Aca, etc.,

the lowest numerical designation' referring to the lowest critical temperature. At these critical temperatures certain allotropic and chemical changes occur which result in consequent physical changes in the metal. For example, when the metal is heated to the temperature Aci, transition from alpha iron to beta iron begins; at Acz,

the blank when' cooled at relatively low temperature will remain on the arbor with the necessary tight fit for accurate machining of the metal. If

the blank so that when it is cooled it will not exl pand or dilatate away from accurate intimate and tight contact with the arbor.

The steel alloys -which are suitable for the fabrication of propeller blades are limited to those the iron loses its magnetic properties; and at Aca, the iron is transformed to its gamma and austenitic phase and this chemical 'change results in an absorption of heat without an increase in temperature. At Aca, also, the steel contracts until the chemical transformation is completed, after which the expansion of the metal with increasing temperature continues. Similar phenomena occur in cooling lthe iron from a high temperature to a low temperature, and with slow cooling; althoughfsince infinitely slow cooling is not possible, the, critical temperatures during cooling which are respectively referred to as Ara. Arr. and Ari are depressed somewhat from their similar critical temperatures during the final heating because of thermal hysteresis. Thus, at the cooling point Ara the contraction which occurs at the heating point Ac: becomes an expansion or dilatation. l.l

The blank is shrunk onto. the arbor from a temperature at least slightly below the heating critical temperature Aca so the transformation-to gamma iron and the corresponding contraction will be avoided, as well as the dilatation on cooling. By heating to a temperature at least slightly less than the upper critical temperature Aca, uninterrupted contraction of the blank onto the arbor is accomplished, and the maximum diametrical expansion and the maximum arbor' clearance are obtained for the shrinking of the blank onto the arbor.

In heating the blank from the temperature extent of this hardening is a function of the maximum temperature reached in the shrinking operation. It is thus desirable to shrink the work on the arbor from a temperature in the vicinity of the lower critical temperature Aci, providing there is adequate expansion to avoid interference between the arbor and the blank with allowance for internal irregularities in theA blank. If the inaccuracies of the blank require heating above Aci to provide adequate arbor clearance, the consequent hardness due to the elevated temperature may be reduced and embarrassment to subsequent machining operations minimized by reducing the cooling rate during the shrink. This may A step of shrinking the tubular blank onto an arbor,

the blank is heated to a temperature slightly less than the Aca temperature which results in complete and uninterrupted contraction of the blank onto the arbor, producing a perfect contact between the blank and the arbor when they are cooled, and this temperature results 1n controlling the hardening characteristics of the material of the blank to promote ease of machining.

When the blank has been thus shrunk and is tightly tted and shaped around the arbor, the arbor with the blank thereon is placed in a lathe 2l for machining the external surface of the blank and relieving diametrically opposite zones e2 on the blank section d to produce reduced wallthickness. 'I'his machining may be done with a cutting tool 25 for milling portions of the blank during the.rotation of the arbor and blank and` in practice is automatically controlled in any manner well understood in the art, to cut away predetermined zones of the desired contour and of varying depth from the blank, usually in the portions of the blank used to form the bladefaces, leaving the portions used for forming the trailing and leading edges of substantially full wall-thickness.

After the blank has been thus machined the arbor with the blank thereon is removed from the lathe and the work is heated to a sufciently high degree for expansion to permit the arbor to be easily withdrawn from the machined blank. This is usually done by placing the blank and core into a cylindrical chamber and delivering a blast of hot gas around the outside of the blank in the chamber. When' the blank has been removed from the arbor, it will shrink so that its internal periphery will conform to the outer periphery of thev arbor and be provided with the desired accurate variations in wall-thickness.V

Next, the tubular blank is subjected to a bending operation to shape its section d, as illustrated in Fig. 8, so that one side d1 of the blank will conform substantially to the curvature desired in the leading edge of the propeller blade.

Next the blank is flattened in a press comprising dies g, g1 to assume the contour illustrated in Fig. and the cross-sectional shape shown in Fig. 9. The blank is then cut oi through bothl faces on dotted line d2, as indicated in Fig. l0, to conform substantially to the desired trailing edge and tip contour. The substantially parallel marginal portions of the blank along the cut edges are passed between welding rolls h, as illustrated in Fig. l1, and the inner faces of the contiguous substantially parallel marginal portions along the A cut are autogenously welded together for a leadsure so the outer faces will be forced into desired external contour.

Next, the leading and trailing edges are shaped to airfoil form and polished or finished to provide smooth faces and'edges. The finished blade is then nitrided to give the metal the desired hardness for wear and strength.

The invention is not to be understood as restricted vto the details set forth, since these may be modified within the scope of the appended claims, without departing from the spirit and Yscope of the invention.

Having thus described the invention, what I claim as new and desire to secure by Letters Patent is:

1. That improvement in the manufacture of hollow propeller blades which comprises heating a tubular blank of medium carbon steel to expand it suiciently to freely receive an arbor having a peripheral dimension which prevents the reception of the blank while it is cold and controlling the temperature during theheating to prevent transformation -oi' the metal into gamma iron, placing the heated blank on the arbor, cooling and shrinking the blank around the arbor so that the metal of the rblank is stretched about the arbor and givena permanent set with the entire inner periphery of the portion of the blank to be used in the forming of the blade faces in conformity'with the shape of the arbor to remove thev irregularities of the inner surface of the blank,cutting away zones of metal from the outer periphery of the blank while it 'is shrunk on the arbor to provide zones of reduced wallthickness in the portion of the blade which is to be formed into the blade faces and leaving longitudinally extending zones of greater wall-thickness for use in forming the edges of the blade, removing the blank from the arbor, and shaping a Iportion of the tubular blank into suction and pressure faces of airfoil contour.

2. That improvement in the manufacture of hollow propeller blades which comprises heating a tubular blank of medium carbon steel to expand it sufficiently to freely receive an arbor having a peripheral dimension which prevents the reception of the blank while it is cold, placing the heated blank on the arbor, cooling and shrinking the blank around the arbor so 'that the metal of the blank is stretched about the arbor and given a permanent set with the entire inner periphery of the portion of the blank to be used in the forming of the blade faces in conformity with the shape of the arbor to remove the irregularities of the inner surface of the blank, cutting away portions of the metal in the outer face of the blank to provide variations in wall-thickness, removing the blank from the'arbor, and shaping a 4portion of the tubular blank into suction and pressure faces of airfoil contour.

3. That improvement in the manufacture of hollow propeller blades which comprises heating a tubular steel blank to expand it sufficiently to freely receive an arbor having a peripheral dimension which prevents the reception of the blank while it is cold and controlling the temperature during the heating to prevent transformation of the metal into gamma iron, placing the heated lblank on the arbor, cooling and shrinking the blank around the arbor so that the metal of the blank is stretched about the arbor and given a permanent set with the entire innerperiphery of the portion of the blank to be used in the forming of the blade faces in conformity with the shape of theyY arbor to remove the irregularities of the inner surface of the blank, cutting oppositely disposed zones of" metal from the outer face of the blank and leaving longitudinally extending zones of greater wall-thickness while it is shrunk on the arbor for providing variations in the wall-thickness of the portions to be used in forming the working faces and edges of the blade, removing the blank from the arbor, and shaping the portions of the blank having varying wall-thickness into suction and pressure faces of airfoil contour.

4. That improvement; in the manufacture of hollow propeller blades which comprises heating to a point -below critical temperature Acaand above the critical temperature Aci a tubular steel blank to expand it suiilciently to freely receive an arbor having a peripheral dimension which prevents .the reception of the blank while it is cold and preventing the transformation of the metal into gamma iron. placing the heated blank on the arbor, cooling and shrinking the blank around the arbor so that the metal of the blank is stretched about the arbor and given a permanent set with the entire inner periphery ot the portion of the blank to be used inthe forming of the blade faces in conformity with the shape of the arbor to remove the irregularities of the inner surface of the blank, cutting zones of metal from the outer face of the blank while it is shrunk on the arbor for providing variations in the wall-thickness of the portions to be used in forming the working portion of the blade, removing the blank from the arbor, and shaping the blank to form suction and pressure faces of airfoil co'ntour.

5. That improvement in the manufacture of hollow propeller blades which comprises heating a tubular steel blank to expand it sulciently to freely receive an arbor having a peripheral dimension which prevents the reception of the blank while it is cold and controlling the tem` perature during the heating to prevent transformation of the metal into gamma iron, placing the heated blank on the arbor, cooling and shrinking the blank around the arbor so that the metal of the blank is stretched about the arbor and given a permanent set with the entire inner periphery of the portion of. the blank to be used in the forming of the blade faces in conformity with the shape of the arbor to remove the irregularities of the inner surfaces of the blank, and controlling the cooling so as to prevent dilation, cutting zones of metal from the outer face of the blank while. it is shrunk on the arbor for providing variations in the wallthickness of the portions to be used in forming the working portion of the blade. removing the blank from the arbor, and shaping the blank to formsuction and pressm'e faces `of airfoil contour.

GLEN T. LAMPTON. 

